Frictional properties of titanium carbide, titanium nitride, and vanadium carbide: Measurement of a compositional dependence with atomic force microscopy

Abstract

The frictional properties of TiC(100), TiN(100), and VC(100) surfaces have been investigated on the microscopic scale by atomic force microscopy. In this work, friction measurements were performed under controlled ambient conditions to emulate the use of these materials as hard coatings. A variety of tip materials, silicon nitride, titanium carbide, titanium nitride, and tungsten carbide, were used to investigate the correlation between surface composition and frictional properties of the carbide and nitride substrates. The surface compositions of both clean and air-exposed samples were characterized by x-ray photoelectron spectroscopy to complete the composition/friction correlation. In these studies, the TiC(100) substrate exhibited the lowest frictional response of the substrate samples, regardless of tip composition. The friction measurements on TiN(100) and VC(100) exhibited a strong dependence on counterface composition and were consistently higher than those of TiC. In addition to the compositional dependence, the influence of humid conditions on the frictional properties of these carbide and nitride substrates has been investigated. The measured friction of each of these samples increased monotonically as a function of relative humidity. The magnitude of these increases has been correlated with the substrate surface free energies as probed by water contact angle measurements.